Playing with stateFn and a stupid counter

main.go

// inspired by
// https://github.com/golang/go/blob/8d7be1e3c9a98191f8c900087025c5e78b73d962/src/text/template/parse/lex.go#L228
package main

import (
	"fmt"
	"log"
)

type stateFn func(s *state) stateFn

type state struct {
	counter     int
	initialized bool
}

func addOne(s *state) stateFn {
	s.counter++
	return addTwo(s)
}

func addTwo(s *state) stateFn {
	s.counter += 2
	return start
}

func start(s *state) stateFn {
	if s == nil {
		log.Println("state must not be nil")
		return nil
	}
	if !s.initialized {
		s.counter = 0
		s.initialized = true
	}
	// counter will be incremented by 3 (1+2)
	if s.counter >= 9 {
		return nil
	}
	return addOne(s)
}

func main() {
	obj := &state{}
	// var obj *state
	for s := start(obj); s != nil; {
		fmt.Printf("running, counter is at %d\n", obj.counter)
		s = s(obj)
	}
	fmt.Println(obj.counter)
}